This research will investigate two major questions in behavioral biology. First, what varied roles does bird song play in the life of a bird? This is one of the most fundamental questions being asked by behaviorists. Second, and equally interesting, why do some birds have very simple song repertoires while others sing varied and complex songs? The song of the white-throated sparrow, Zonotrichia albicollis, may play a role in the reproductive stimulation of mates, territory defense, and the attraction of mates. Its song may also act to disrupt the foraging behavior or neighboring males. These proposed functions of song will be investigated. This research will also test if white-throated sparrows use their one song-type in ways analagous to species with more than one song in an individual's repertoire. They might do this by varying completeness, loudness, and song rate. The reproductive stimulation function of song will be tested by playing songs to captive females previously treated with estradiol and quantifying the number and intensity of copulation solicitation displays. The territory defense function of song will be tested by using speaker-replacement and standard playback experiments. The attraction-of-mates function of song will be tested by (1) surgically devocalizing males before they have attracted females; and (2) determining if females are attracted to playbacks of males' song before they have paired. Other specific aims of this project are to determine if neighbor singing disrupts the foraging behavior of territory holders and to determine if territorial defense and foraging are competing activities in the time budget of white-throated sparrows.